Glass composition, structure, and apparatus using the same

ABSTRACT

Provided are a glass such as a sealing glass which contains a rare earth element and crystalline particles, a structure made by sealing with said sealing glass, a magnetic head made by bonding using said sealing glass, and a magnetic recording and reproducing apparatus on which said magnetic heads are mounted. According to the glass of the present invention, magnetic heads, and other structures can be bonded at low temperatures and a high bond strength can be attained, and thus, magnetic heads having high-speed sliding properties and magnetic recording and reproducing apparatuses of high reliability can be obtained. The glass can be also used for heat resistant parts such as a pannel glass for a cathode-ray tube and the like.

BACKGROUND OF THE INVENTION

The present invention relates to a glass material, in particular, asealing glass, and a magnetic head made by bonding with the sealingglass and a magnetic recording and reproducing apparatus using themagnetic head. Moreover, the glass material of the present invention canhave a high strength without increasing a melting point. Therefore, theglass material can be also used for heat resistant parts such as apannel glass for a cathode-ray tube and a Pyrex glass, and additionally,can be further used for a pannel glass for a liquid crystal display.

Hitherto, a sealing glass which can be handled at a temperature lowerthan the resisting temperature of various parts has been used forbonding of core materials of magnetic heads to be mounted on magneticrecording and reproducing apparatuses such as VTR or bonding ofsemiconductor sensors, covering of electronic circuit parts such as ICand LSI, and sealing of electron tubes. When the resisting temperatureof the parts is high, sealing glasses of SiO₂ --B₂ O₃ type or PbO--SiO₂type are used which are relatively high in chemical endurance ormechanical strength, but when the resisting temperature is low, sealingglasses of PbO--B₂ O₃ type are mainly used.

At present, in the case of magnetic heads for VTR, single crystal Mn--Znferrites having a saturated magnetic flux density (Bs) of about 5000gausses are used as the magnetic core materials. Since the resistingtemperature of these ferrites is about 800° C., glasses of PbO--SiO₂--R₂ O type or ZnO--B₂ O₃ --SiO₂ --R₂ O--RO type which can perform thebonding at 700-800° C. are used as the bonding glass. Here, R₂ O meansan alkali metal oxide and RO means an alkaline earth metal oxide. Withrecent development in higher performance magnetic recording andreproducing apparatuses and high-recording density magnetic recordingmedia, Co-based amorphous metal magnetic films or sendust alloy filmshaving a Bs of about 10000 gausses and magnetic films mainly composed ofiron element and having a Bs of 12000 gausses or more, such as Fe--N orFe--C magnetic films, have been developed for magnetic heads.

These magnetic films have a high saturated magnetic flux density whilethey are considerably lower in resisting temperature than Mn-Znferrites. Therefore, the bonding temperature is lower than 480° C. forCo-based amorphous metal magnetic films, about 600° C. for sendust alloyfilms, 500-550° C. for Fe--N magnetic films, and 550-600° C. for Fe--Cmagnetic films. Thus, a PbO--B₂ O₃ sealing glass which can perform thebonding at lower than these resisting temperatures is used as disclosedin JP-A-63-170240, JP-A-63-298807, JP-A-3-265539, JP-A-2-184541,JP-A-2-258649, etc. Moreover, it is proposed to use a V₂ O₅ --P₂ O₅sealing glass as disclosed in JP-A-4-132634.

In the above conventional techniques, no sufficient consideration hasbeen taken to satisfy simultaneously the three conditions of bondingability at low temperatures of lower than 600° C., sufficient mechanicalstrength and sufficient deaeration. Recently, the demand for highdensity recording of magnetic recording and reproducing apparatuses isfurther increased and the magnetic heads mounted thereon are required tohave a high output and a sufficient strength to stand the use underfurther severer conditions. As magnetic core materials which can meetthe demands, Fe--C or Fe--N magnetic films very high in saturatedmagnetic flux density are studied, and, hence, glasses which can carryout sealing at low temperatures of lower than 600° C. must be used.

Furthermore, in order to improve tape touch between the magnetic headand the magnetic recording medium, the sliding width between themagnetic head and the magnetic recording medium must be reduced.Moreover, in order to increase recording capacity, the relative speed ofthe magnetic head and the magnetic recording medium must be markedlyincreased than usual.

For these reasons, the glass bonding part of magnetic heads is exposedto the severer use atmosphere. Therefore, the conventional sealing glasscapable of performing the bonding at low temperatures are insufficientin mechanical strength and breakage sometimes occurs from the glassbonding part during the sliding of tape. That is, the glasses disclosedin JP-A-63-170240, JP-A-63-298807 and JP-A-3-265539 are insufficient inmechanical strength and can hardly stand the above-mentioned useatmosphere.

The sealing glasses disclosed in JP-A-2-184541 and JP-A-2-258649 aresuperior in mechanical strength, but since they contain manycrystallizing components, viscosity of the glass can be adjusted withdifficulty and deaeration can be controlled with difficulty. The sealingglass disclosed in JP-A-4-132634 contains P₂ O₅ and there is thepossibility of generation of bubbles produced by water contained in thestarting materials.

JP-A-1-138150 discloses a low melting point glass mainly composed ofPbO, TeO₂, P₂ O₅ and the like, and containing fluorine and rare earthmetal oxides, i.e., Y₂ O₃, La₂ O₃ and Gd₂ O₃. However, it is hard toenhance the strength of this type of a glass because the rare earthmetal oxides are incorporated into the glass structure and crystallineparticles are not generated owing to P₂ O₅ and fluorine containedtherein.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sealing glassexcellent in low-temperature bonding ability, high in mechanicalstrength and less in generation of bubbles, a method for producing theglass, and a structure made using the glass.

Another object of the present invention is to provide a magnetic head ofhigh performance and high reliability which can stand severe conditionssuch as use in high-vision digital VTR and others and a method formaking the same, and a magnetic recording and reproducing apparatus ofhigh performance and high reliability on which the magnetic head ismounted.

According to the present invention, there is provided a glass containinga rare earth element and crystalline particles. The glass can be usedfor a sealing glass and heat resistant parts such as a pannel glass fora cathode ray tube and the like.

The sealing glass of the present invention for attaining the aboveobjects is a sealing glass containing at least one rare earth elementand, in this glass, fine particles are uniformly dispersed in itsmatrix. Said fine particles contain at least one of rare earth elements.These rare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yband Lu. Furthermore, the fine particles have a particle size of 1-50 nm,more preferably 3-10 nm. Moreover, the fine particles are crystalline.Said matrix contains a heavy metal oxide and boron oxide and/or siliconoxide. The heavy metal oxide is preferably an oxide of lead.

The sealing glass of the present invention contains, in terms of thefollowing oxides, PbO: 44-91% by weight, B₂ O₃ : at least 6% by weight,SiO₂ : 0-30% by weight, the total content of B₂ O₃ and SiO₂ : 6-40% byweight and Ln₂ O₃ (Ln: Pr, Nd, Sm. Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb andLu): 0.3-2.9% by weight, and fine particles are uniformly dispersedtherein. More preferably, the sealing glass contains, in terms of thefollowing oxides, PbO: 44-77% by weight, B₂ O₃ : 6-20% by weight, SiO₂ :0-30% by weight, the total content of B₂ O₃ and SiO_(2:) 6-40 % byweight, at least one of ZnO, Al₂ O₃ and R₂ O (R: an alkali metalelement): 0-25% by weight and Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb and Lu): 0.5-1.5% by weight, and the fine particles areuniformly dispersed therein.

Furthermore, the sealing glass of the present invention is a sealingglass containing at least one of rare earth elements, and in this glass,fine particles and low-expansion fillers are uniformly dispersed in thematrix. Said fine particles contain at least one of the rare earthelements. The rare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho,Er, Tm, Yb and Lu. The fine particles have a particle size of 1-50 nmand the matrix contains an oxide of lead and boron oxide and/or siliconoxide. The low-expansion filler is at least one of zirconium silicate,lead titanate, β-eucryptite, and silica glass.

The method for producing the glass according to the present inventionincludes a step of heating a mixed powder of glass raw materials in acrucible to obtain a glass melt, a step of precipitating fine particlesin the glass melt, a step of continuously stirring the glass melt byvibration generated by a vibrator provided in contact with outer wall ofthe crucible, a step of cooling the glass melt to obtain a glass, and astep of reheating the glass and annealing it. The raw materials for theglass contain the elements of rare earth, lead, and boron and/orsilicon. The rare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb and Lu. The fine particles have a particle size of 1-50nm.

Furthermore, the structure of the present invention comprises at least asubstrate and a sealing glass coated on the surface thereof, and thissealing glass contains at least one of rare earth elements and comprisesa matrix in which fine particles are uniformly dispersed. The structurefurther comprises at least a pair of substrates and a sealing glassprovided therebetween. The pair of the substrates are bonded with thesealing glass, and this sealing glass contains at least one of rareearth elements and comprises a matrix in which fine particles areuniformly dispersed.

Said fine particles contain at least one of rare earth elements. Therare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb andLu. The fine particles have a particle size of 1-50 nm and the matrixcontains an oxide of lead and boron oxide and/or silicon oxide.

Next, the magnetic head of the present invention comprises a pair ofmagnetic cores, a non-magnetic gap material provided between themagnetic cores and a sealing glass which bonds the pair of the magneticcores. This sealing glass contains at least one of rare earth elementsand comprises a matrix in which fine particles are uniformly dispersed.The fine particles contain at least one of the rare earth elements. Therare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb andLu. The fine particles have a particle size of 1-50 nm, preferably 3-10nm, and the matrix contains an oxide of lead and boron oxide and/orsilicon oxide.

The magnetic head of the present invention comprises a pair of magneticcores, a non-magnetic gap material provided between the magnetic coresand a sealing glass which bonds the pair of the magnetic cores. Thesealing glass contains, in terms of the following oxides, PbO: 44-77% byweight, B₂ O₃ : 6-20% by weight, SiO₂ : 0-25% by weight, the totalcontent of B₂ O₃ and SiO₂ : 6-30% by weight, Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu): 0.5-1.5% by weight and the remainderof at least one of Al₂ O₃, ZnO and R₂ O (R: an alkali metal element),and fine particles are uniformly dispersed therein. The above sealingglass has a micro Vickers hardness Hv of 425 or higher. Said magneticcore comprises a support on which a magnetic film is formed, and morepreferably, the magnetic film is a Fe-based film.

The magnetic head of the present invention comprises a pair of magneticcores on which magnetic films are formed, only the gap part beingbutting faces, a non-magnetic gap material provided between the pair ofthe magnetic cores and a sealing glass, and this sealing glass bonds thebutting faces to each other. The sealing glass contains at least one ofrare earth elements and this glass comprises a matrix in which fineparticles are uniformly dispersed. Said fine particles contain at leastone of rare earth elements. The rare earth elements are Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu. The fine particles have a particlesize of 1-50 nm, more preferably 3-10 nm. Said matrix contains an oxideof lead and boron oxide and/or silicon oxide. More preferably, themagnetic film is Fe-based film. It is preferred that the sliding widthbetween the magnetic head and the recording medium is 65 μm or less.

The method for making the magnetic head according to the presentinvention includes a step of forming a non-magnetic gap material at thebutting part of at least a pair of magnetic cores, a step of butting thepair of the magnetic cores, a step of sealing them with a sealing glasscontaining at least one of the rare earth elements, and a step ofprecipitating fine particles in the sealing glass. The step ofprecipitating the fine particles is conducted by a heat treatment at atemperature lower than the resisting temperature of the magnetic cores.The fine particles contain at least one of rare earth elements. The rareearth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.The fine particles have a particle size of 1-50 nm, more preferably 3-10nm. The sealing glass contains an oxide of lead and boron oxide and/orsilicon oxide.

The magnetic recording and reproducing apparatus of the presentinvention is provided with at least magnetic heads comprising a pair ofmagnetic cores composed of a support on which a magnetic film is formed,said magnetic cores being bonded with a sealing glass through anon-magnetic gap material, a cylinder part fitted with a plurality ofthe magnetic heads, a driving part for the cylinder part, and a controlpart carrying out the information processing from the informationrecording medium. The sealing glass contains at least one of rare earthelements and comprises a matrix in which fine particles are uniformlydispersed.

The fine particles contain at least one of the rare earth elements. Therare earth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb andLu. Furthermore, the fine particles have a particle size of 1-50 nm,more preferably 3-10 nm. Said matrix contains an oxide of lead and boronoxide and/or silicon oxide.

Furthermore, the magnetic recording and reproducing apparatus of thepresent invention is provided with a magnetic head constructed of a pairof magnetic cores having magnetic films, only the gap parts thereofbeing butting faces, a non-magnetic gap material provided between thepair of the magnetic cores and a sealing glass which bonds the buttingfaces to each other; a jig for fitting one or more of the magneticheads; a cylinder part fitted with a plurality of the fitting jigs; adriving part for the cylinder part; and a control part which carries outprocessing of information from the information recording medium. Thesealing glass contains at least one of rare earth elements and comprisesa matrix in which fine particles are uniformly dispersed. The fineparticles contain at least one of said rare earth elements, and the rareearth elements are Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.Furthermore, the fine particles have a particle size of 1-50 nm, morepreferably 3-10 nm. Said matrix contains an oxide of lead and boronoxide and/or silicon oxide. In the magnetic head mounted on the magneticrecording and reproducing apparatus of the present invention, themagnetic film is preferably Fe-based film, and desirably, the slidingwidth between the magnetic head and the recording medium is 65 μm orless. Moreover, the relative speed of the magnetic head and therecording medium is preferably 20 m/sec or more.

The present invention resides in a sealing glass, characterized in thatthe glass comprises, in terms of the following oxides and by weight,30-93% of PbO, 25% or less of B₂ O₃ and 30% or less of SiO₂ and has amicro Vickers hardness of 370 or higher and the viscosity of the glassreaches 104 poises at 600° C. or lower.

Furthermore, the present invention resides in the above sealing glass,characterized in that the glass additionally contains at least one of10% or less of Al₂ O₃, 15% or less of ZnO, 15% or less of Na₂ O, 15% orless of K₂ O, 15% or less of Bi₂ O₃, 10% or less of TeO₂, 10% or less ofFe₂ O₃, 5% or less of SrO and 5% or less of TiO₂ and, optionally, Ln₂ O₃(Ln is at least one of Sc, Y, La and lanthanides).

The present invention resides in a high-definition magnetic recordingand reproducing apparatus, characterized in that the apparatus isprovided with magnetic heads comprising a pair of magnetic corescomposed of a magnetic film formed on a support, said magnetic coresbeing bonded to each other with a sealing glass through a non-magneticgap material; a cylinder part fitted with a plurality of the magneticheads; a driving part for the cylinder part; and a control part whichcarries out processing of the information from the information recordingmedium comprising a tape having a metal magnetic film, and that therelative speed of the cylinder part and the information recording mediumis 20 m/sec or higher or 50 m/sec or higher, the sliding width betweenthe magnetic head and the information recording medium is 65 μm or less,and the time required for breaking the magnetic head by rotation of thecylinder part and sliding with the information recording medium is 500hours or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph which shows the relation between the atomic number ofthe rare earth elements contained in the glass and the deformationtemperature of the glass.

FIG. 2 is a graph which shows the relation between the atomic number ofthe rare earth elements contained in the glass and the micro Vickershardness of the glass.

FIG. 3 is a graph which shows the relation between the content of therare earth oxides and the deformation temperature of the glass.

FIG. 4 is a graph which shows the relation between the content of therare earth oxides and the micro Vickers hardness of the glass.

FIG. 5 is a graph which shows the relation between the content of therare earth oxides and the particle size of fine particles present in theglass.

FIG. 6 is a graph which shows the relation between the particle size offine particles and the micro Vickers hardness.

FIG. 7 is an oblique view of a structure of the present invention.

FIG. 8 shows the method for bonding the structure shown in FIG. 7.

FIG. 9 shows the method for the measurement of the bond strength.

FIGS. 10 and 11 are photographs of the glass No. 14 taken by atransmission electron microscope.

FIG. 12 is a graph which shows the composition of PbO--SiO₂ +B₂ O₃.

FIG. 13 is a graph which shows the relation between the Vickers hardnessand the amount of SiO₂ +B₂ O₃.

FIG. 14 is a graph which shows the relation between the Vickers hardnessand the deformation temperature Td.

FIG. 15 is an oblique view of a magnetic head of the present invention.

FIG. 16 is an oblique view of a magnetic head having the magnetic filmaccording to the present invention.

FIG. 17 shows the procedure of making a magnetic head.

FIG. 18 shows the procedure of making a magnetic head.

FIG. 19 shows the procedure of making a magnetic head.

FIG. 20 shows a jig for measuring the strength of head chip.

FIG. 21 is an oblique view of a magnetic head of the present invention.

FIG. 22 is an oblique view of a magnetic head of the present invention.

FIG. 23 shows a fitting method of the magnetic head according to thepresent invention.

FIG. 24 is a block diagram of a magnetic recording and reproducingapparatus of the present invention.

FIG. 25 is an oblique view of a rotating drum mounted with the magnetichead of the present invention.

FIG. 26 is a front view of a rotating drum mounted with the magnetichead of the present invention.

FIG. 27 is a diagram of a high-definition multi-system.

FIG. 28 is a block diagram of a 6 mm digital VCR of the presentinvention.

FIG. 29 is a block diagram of a 6 mm digital videocassette of thepresent invention.

FIG. 30 is a block diagram of a transmission electron microscope of thepresent invention.

FIG. 31 is a block diagram of a scanning electron microscope of thepresent invention.

In these drawings, the main reference numerals indicate the following.

1: Sealing glass; 2, 2': Materials to be bonded; 11, 11': Magneticcores; 14, 14': Magnetic films; 15: Magnetic gap; 16: Sealing glass; 18,18': Coils; 19: Fitting jig; 20: Terminal guiding hole; 21: Video head;22; Cylinder; 26: Magnetic recording medium.

DETAILED DESCRIPTION OF THE INVENTION

The glass of the present invention is a glass containing at least onerare earth element and this glass comprises a matrix in which fineparticles are uniformly dispersed, thereby to make it possible toimprove sharply the mechanical strength with causing substantially nodeterioration in flowability or deaeration of the glass. The glass canbe used for a sealing glass and heat resistant parts such as a pannelglass for a cathode-ray tube, and the like. Said fine particles containat least one of rare earth elements. As the rare earth elements, Pr, Nd,Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu are effective. Furthermore, itis effective for the fine particles to have a particle size of 1-50 nm.If the particle size is smaller than 1 nm, the effect to improvemechanical strength is small and if it exceeds 50 nm, it is difficult toobtain satisfactory flowability or deaeration of the glass. The particlesize is more preferably 3-10 nm to obtain further superior mechanicalstrength. Moreover, the mechanical strength can be effectively improved,when said matrix is composed of a glass containing a heavy metal oxidesuch as lead oxide and boron oxide and/or silicon oxide, which canperform the sealing at low temperatures.

The sealing glass of the present invention contains, in terms of thefollowing oxides, PbO: 44-91% by weight, B₂ O₃ : at least 6% by weight,SiO₂ : 0-30% by weight, the total content of B₂ O₃ and SiO₂ : 6-40% byweight, and Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb andLu): 0.3-2.9% by weight, and fine particles are uniformlydispersed-therein. Therefore, the resulting glass is excellent inflowability and deaeration and in mechanical strength.

When the PbO content is less than 44% by weight or exceeds 91% byweight, vitrification occurs with difficulty. When the content of B₂ O₃is less than 6% by weight, the fine particles containing rare earthelements cannot be uniformly dispersed in the glass. When the content ofSiO₂ exceeds 30% by weight or the total content of B₂ O₃ and SiO₂ isless than 6% by weight, the rare earth oxide powder added remain in theglass in the form of the powder. Moreover, when the total content of B₂O₃ and SiO₂ exceeds 40% by weight, the tendency of vitrificationincreases. When the content of Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu, Gd, Tb, Dy,Ho, Er, Tm, Yb and Lu) is less than 0.3% by weight, the effect toimprove the mechanical strength is small and when it exceeds 2.9% byweight, the flowability and deaeration of the glass are unsatisfactory.

Moreover, when the content of PbO in the above ranges exceeds 77% byweight, the effect to improve the mechanical strength by adding the rareearth elements is small. Further, when the B₂ O₃ content exceeds 20% byweight, also the effect to improve the mechanical strength is small.When ZnO and Al₂ O₃ are contained, chemical stability and mechanicalstrength of the glass are further improved. When R₂ O (R: an alkalimetal element) is added, the glass can be rendered low-melting. Thealkali metal elements here include elements such as, for example,lithium, sodium, potassium, rubidium and cesium. However, if the totalcontent of ZnO, Al₂ O₃ and R₂ O exceeds 25% by weight, the glass iscrystallized. Moreover, when the content of Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) is less than 0.5% by weight orexceeds 1.5% by weight, the effect to improve the mechanical strength issmall.

Therefore, more preferably, the sealing glass contains, in terms of thefollowing oxides, PbO: 44-77% by weight, B₂ O₃ : 6-20% by weight, SiO₂ :0-30% by weight, at least one of ZnO, Al₂ O₃ and R₂ O (R: an alkalimetal element): 0-25% by weight, and Ln₂ O₃ (Ln: Pr, Nd, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb and Lu): 0.5-1.5% by weight.

Furthermore, according to the present invention, the apparent thermalexpansion coefficient of the sealing glass can be reduced by uniformlydispersing in the matrix the low-expansion fillers such as, for example,zirconium silicate, lead titanate, β-eucryptite and silica glass, and,thus, the glass can be applied to the sealing of low-expansionmaterials.

The sealing glass of the present invention can be produced by a methodincluding a step of heating a mixed powder of glass raw materials in acrucible to obtain a glass melt, a step of precipitating fine particlesin the glass melt, a step of continuously stirring the glass melt byvibration generated by a vibrator provided in contact with outer wall ofthe crucible, a step of cooling the glass melt to obtain a glass, and astep of reheating the glass and annealing it.

Since the sealing glass of the present invention has good mechanicalstrength, flowability and deaeration, a structure sealed using thisglass can be greatly improved in reliability. Therefore, the glass isvery effective for structures such as a magnetic head.

Next, since the sealing glass of the present invention is excellent inflowability at low temperatures, magnetic films mainly composed of Fewhich are low in heat resistance, but high in saturated magnetic fluxdensity can be used, and as a result, magnetic heads excellent in boththe reliability and the performance can be obtained. Especially, whenthe sealing glass has a micro Vickers hardness of 425 or more, yield inproduction of magnetic heads is high and strength of head chips is high,and magnetic heads of long life can be obtained even when the relativespeed of the magnetic head and the magnetic recording medium is higherthan 52 m/sec.

Furthermore, by using the sealing glass of the present invention, thesliding width of the magnetic head can be reduced to 65 μm or less, andas a result, improvement of performances due to improvement of tapetouch and maintenance of reliability can be attained. Moreover, thesealing glass of the present invention makes it possible to bond onlythe gap parts of magnetic head and greatly simplify the coil windingstep of magnetic heads.

Moreover, the magnetic recording and reproducing apparatus provided withthe magnetic heads of the present invention can be markedly improved inperformance and reliability. Further, the magnetic heads can be appliedto magnetic recording and reproducing apparatuses of 20 m/sec or higherin the relative speed of the magnetic head and the magnetic recordingmedium, such as high-definition digital VCR.

From the points of proper thermal expansion coefficient and bondingtemperature, in the bonding glass for magnetic heads, there may be used55-70% of V₂ O₅, 17-25% of P₂ O₅, 3-20% of Sb₂ O₃, 0-20% of PbO, 0-15%of Tl₂ O and 0-5% of Nb₂ O₅ (by weight).

SiO₂ is mainly used as the non-magnetic gap material, and an SiO₂ --B₂O₃ glass, an SiO₂ --PbO glass and the like which have a bondingtemperature in the range of 700-800° C. are used for bonding of themagnetic cores.

Magnetic films such as of Co-based amorphous alloys, sendust alloys andFe-C materials having a saturated magnetic-flux density higher than thatof ferrites are used for the magnetic cores as shown in Table 1. Thesaturated magnetic flux density of these magnetic films is higher than8000 gausses, which is considerably higher than 4000-5000 gausses offerrites. Therefore, high density recording much higher than thatobtained by conventional magnetic heads can be obtained using themagnetic heads which use the above-mentioned magnetic films.

As shown in Table 2, the substrate is needed to have a micro Vickershardness of at least 600 from the point of wear resistance of magneticheads. Furthermore, since the substrate must have a thermal expansioncoefficient adapted to that of the magnetic film to some extent,combinations of the substrate a-c shown in Table 2 with the magneticfilm A shown in Table 1, the substrates e and f shown in Table 2 withthe magnetic film B shown in Table 1, and the substrates c and d shownin Table 2 with the magnetic film C shown in Table 1 are preferred.

The present invention can be applied to extended definition digital VCRfor business use, extended definition 6 mm digital VCR for public use,digital videocassettes for public use, analog 8 mm-VCR, S-VHS andW-VES-VCR.

                  TABLE 1                                                         ______________________________________                                                     Saturated                                                          magnetic Thermal                                                              flux expansion Resisting                                                      density coefficient temperature                                             Magnetic film  (tesla)  (×10.sup.-7 /° C.)                                                         (° C.)                               ______________________________________                                        A    Co-based amorphous                                                                          0.9      120     480                                          alloy                                                                         (Co--Nb--Zr)                                                                 B Sendust alloy 1.0 150 620                                                    (Fe--Si--Al)                                                                 C Fe--C material 1.5 130 620                                                   (Fe--C--Ta)                                                                  D Single crystal 0.5 110 800                                                   Kn--Zn ferrite                                                             ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                                        Thermal expan-                                                                         Micro                                                  sion coefficient Vichers                                                    Substrate         (×10.sup.-7 /° C.)                                                          hardness Hv                                      ______________________________________                                        a     Single crystal Mn--Zn                                                                         110        650                                             ferrite                                                                      b α-Fe.sub.2 O.sub.3 ceramics 115 900                                   c NiO--CoO--TiO.sub.2 120 650                                                  ceramics                                                                     d MgO--NiO ceramics 130 800                                                   e MnO--NiO ceramics 135 600                                                   f TiO.sub.2 --NiO--CaO 140 850                                                 ceramics                                                                   ______________________________________                                    

DESCRIPTION OF THE PREFERRED EMBODIMENTS EXAMPLE 1

Table 3 shows blending composition (% by weight) of the glassinvestigated in the present invention, kind of the added rare earthelements (Ln), glass transition temperature (Tg/° C.) and deformationtemperature (Td: ° C.) measured from thermal expansion characteristics,and micro Vickers hardness (Hv: kgf-mm⁻²) of the glass. It further showsthe state of vitrification at the time of making the glass and the stateof a structure made using this glass. Both the Tg and the Td can beobtained from a chart which shows the relation between elongation andtemperature. Tg is shown by the point at which the elongation firstabruptly increases and Td is shown by the point at which the elongationis saturated. The sample has 5 mmφ and the measurement is conductedunder application of a load of 10 g.

The glass was produced in the following manner. Raw material powders ina given amount were weighed and charged in a platinum crucible and mixedtherein, followed by melting the mixture at about 1000-1100° C. in anelectric furnace. After the raw materials were sufficiently molten, themelt was stirred for about 1 hour by generating an ultrasonic in themelt by an ultrasonic generator provided at the hearth. Then, the glassmelt was poured into a graphite mold heated at about 300° C. to make aglass block. The glass block was annealed at 5° C./min or less,preferably 1-2° C./min and processed to prepare various test pieces.

                                      TABLE 3                                     __________________________________________________________________________    No.   1  2  3  4  5   6  7  8  9  10 11 12 13 14 15 16 17                     __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55                        SiO.sub.2 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                  B.sub.2 O.sub.3  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8                                                                  Al.sub.2 O.sub.3                                                             2  2  2  2  2  2                                                              2  2  2  2  2  2                                                              2  2  2  2  2                                                                  ZnO  7  6  6  6                                                              6  6  6  6  6  6                                                              6  6  6  6  6  6                                                              6                        Na.sub.2 O  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8  8                 Ln.sub.2 O.sub.3 --  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1                                                                 Ln -- Sc Y La Ce                                                             Pr Nd Sm Eu Gd Tb                                                             Dy Ho Er Tm Yb Lu                                                              Tg (° C.)                                                             386  392  385  386                                                             380  378  378                                                                372  375  376  370                                                             373  377  379                                                                374  373  373                                                                  Td (° C.)                                                             422  420  423  421                                                             427  425  427                                                                418  421  420  418                                                             420  421  418                                                                422  421  420                                                                  Hv 395  415  419                                                             420  431  451  434                                                             472  490  496                                                                486  488  489  462                                                             484  474  473                                                                 Vitrification                                                                ◯                                                                 ◯                                                                 ◯                                                                 ◯ X                                                               ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                  Structure                                                                    ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 Bubbles .largecircl                                                           e. ◯                                                              ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯          __________________________________________________________________________

The thermal expansion characteristic was measured using a test piece of5 mmφ×30 mmH at a heating rate of 5° C./min in the air. A silica glasswas used as a standard sample. The micro Vickers hardness was measuredat ten portions under the conditions of a load of 100 g and a loadapplication time of 15 seconds and the average value was employed as themicro Vickers hardness. In the column of vitrification in Table 3, "∘"means that the melt vitrified at the time of glass making and "x" meansthat the melt insufficiently vitrified or did not vitrify. Withreference to the structure in Table 3, the structure illustrated in FIG.7 was made and flowability, deaeration and transparency of the glasswere evaluated and "∘" means that the results of evaluation weresatisfactory and when the results were unsatisfactory, the causetherefor was mentioned.

FIG. 8 illustrates the method of making this structure. An Mn--Znferrite single crystal substrate of a=14 mm, b=7 mm and c=1 mm havingmany rectangular grooves of 0.3 mm in both the depth d and the width ewhich were cut in the direction of b was employed as a material 2 to bebonded. On the grooved surface of the material 2 as a base was placed aplate comprising sealing glass 1 having the same size as the base,followed by carrying out a heat treatment to obtain a structure as shownin FIG. 7. The heat treating conditions were 580° C. at which theviscosity of the glass reached 10⁴ poises and 30 minutes. The atmospherewas under vacuum.

The glass No.1 was a basic glass containing lead oxide, silicon oxideand boron oxide as main components and containing no rare earth element.The glass compositions of Nos.2-17 were determined by replacing 1% byweight of ZnO component of the glass No.1 with oxides of rare earthelements.

As for the glass of No. 5, the added Ce remained in the glass in theform of a powder and a uniform glass could not be made. Accordingly, thevalues shown in Table 3 were those obtained by carrying out themeasurements on the glass in the state of the powder remaining. Otherglasses were satisfactory without causing devitrification, etc. duringmaking of the glass.

FIG. 1 and FIG. 2 show change of the deformation temperature and themicro Vickers hardness of each glass in respect to the atomic number ofthe rare earth elements contained in the glass shown in Table 3. Asshown in FIG. 1, the deformation temperature of the glasses containingany rare earth elements was nearly the same as that of the glass No. 1,namely, it was about 420° C. and constant. Furthermore, it was foundthat as shown in FIG. 2, the micro Vickers hardness of all the glassesincreased as compared with the glass No. 1 containing no rare earthelement. Especially, in the case of the glasses of No.6 to No. 17containing the rare earth elements of Pr and those larger in atomicnumber, the micro Vickers hardness was higher about 10-26% than that ofthe glass No. 1. Thus, it can be seen that only the micro Vickershardness can be increased without increasing the characteristictemperature of the glass by adding rare earth elements.

Moreover, when glass was prepared under continuous stirring byultrasonic as mentioned above, fluctuation in the micro Vickers hardnesswas small while when the glass was prepared without the continuousstirring, the micro Vickers hardness greatly fluctuated. Therefore, itis desirable to carry out the continuous stirring for obtaining sealingglass of high reliability.

Next, the effect of improvement in mechanical strength was evaluated bythe three-point bending test as shown in FIG. 9. As the samples, glassNo.1 and glass No.14 containing 1.0% by weight of Er₂ O₃ were used. Testpieces of 1 mm thick, 2 mm wide and 3 mm long were prepared from theglass blocks. The test piece was set in a measuring jig having an lowerspan of 1.2 mm and the three-point bending strength was measured. Themeasuring number n' was 16 for all samples. When the load applied is w(N), the three-point bending strength σ (MPa) is σ=(3nw/21m²), wherein nis the lower span length, l is the width of the test piece and m is thethickness of the test piece.

The average value of the three-point strengths (σ/MPa) of each sample isshown in Table 4. The average three-point bending strength of the glassNo.1 containing no rare earth element was 70 MPa while that of the glassNo.14 containing Er was 102 MPa, which showed improvement of about 45%.Thus, not only the micro Vickers hardness, but also the three-pointbending strength could be greatly improved by the addition of the oxidesof rare earth elements.

                  TABLE 4                                                         ______________________________________                                        No.      n'          σ(MPa)                                                                          Note                                             ______________________________________                                         1       16           70     Comparative                                           Example                                                                    14 16 102 Example                                                           ______________________________________                                    

As explained above, the mechanical strength can be improved withoutincreasing the characteristic temperature by adding rare earth elements.In order to elucidate the cause therefor, the difference in the innerstructure of glasses due to the presence or absence of rare earthelement was examined by a transmission electron microscope. The glassNo. 14 containing Er₂ O₃ and the glass No.1 containing no rare earthelement were observed by a transmission type electron microscope to findthat the glass No. 1 was wholly uniform amorphous substance while in thecase of the glass No. 14, fine particles having a particle size of about4.5 nm were seen in an amorphous matrix. FIG. 10 is a photograph of theglass No. 14C taken by a transmission electron microscope. Portionsdarker than the matrix are the particles containing the rare earthelement. Point analysis by EDS showed that the particles contained Er ina large amount. According to observation under the higher magnification,a lattice image which shows that the particles are crystalline wasobserved. FIG. 11 is a photograph of the particles and the neighborhoodthereof taken by a transmission electron microscope. In the particles,lattice patterns are observed, and hence the particles are crystalline.In contrast, no lattice pattern is observed in the neighborhood of theparticles. Therefore, it is recognized that the neighborhood isamorphous, i.e., glassy. From this fact, it can be guessed that the fineparticles are fine crystal grains produced with Er of Er₂ O₃ as nuclei.

Moreover, it can be considered that since the particle size of Er₂ O₃raw material powder was about 1 μm, the Er₂ O₃ powder was once dissolvedin the glass melt and, thereafter, exceeded the saturation solubility bycooling of the melt and precipitated in the glass to result in formationand growth of nuclei to produce the fine particles mentioned above.

Furthermore, bonding species of the glass was identified by FT-IR andthere was seen substantially no difference between the glass No.14containing Er₂ O₃ and the glass No.1 containing no Er₂ O₃. From theabove, it is considered that since the bond of glass does not change somuch by the addition of rare earth elements, they do not affect so muchthe characteristic tempera- ture, but propagation of cracks wasinhibited and the mechanical strength was improved due to the presenceof fine particles in the order of several nanometers in the glass.

As mentioned above, glasses which contain at least one of rare earthelements and in which fine particles are uniformly dispersed can beimproved in their mechanical strength without increasing thecharacteristic temperature. In addition, the above rare earth elementsare present much in the fine particles and are essential components forproducing the particles. Therefore, when the rare earth element added iscontained in the fine particles, the fine particles can be moreuniformly contained in the glass.

Among the rare earth elements, Ce also improves the mechanical strengthof the glass without increasing the characteristic temperature, butsince Ce powder remains in the glass as it is, this is not preferred. Itis considered that this is because other rare earth ions are trivalentwhile Ce is tetravalent and stable and, hence, Ce oxide differs fromother rare earth oxides in solubility in glass.

The structure of FIG. 7 was further produced. In the case of glass No.5,the powder remained in the glass and, hence, deaeration was notsatisfactory. Other glasses were superior in flowability, deaeration andtransparency of the glass. Therefore, these glasses can be also used forstructures which are required to have transparency of glass, such asmagnetic head and others.

Sc, Y and La were small in increasing rate. Pm is present only as aradioactive isotope and is difficult to put to practical use. From theabove, it is preferred to use Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yband Lu.

EXAMPLE 2

Next, various characteristics of glass in relation with contents of theoxides of rare earth elements examined in Example 1 are investigated inthis Example. In this Example, three kinds of oxides containing Pr, Ndand Er are investigated. Method of preparation of glass and evaluationmethod are the same as in Example 1.

As shown in the column of "vitrification" in Table 5, when 4.0% byweight of the oxide of the rare earth element was contained (Nos. 6F, 7Fand 14F), no vitrification occurred. When the oxide was contained in anamount of 3% by weight or more (Nos. 6E, 6F, 7E, 7F, 14E and 14F), theflowability and the deaeration of the glass were unsatisfactory at thetime of making the structure. When the content was 2.9% by weight (Nos.6D, 7D and 14D), the flowability of the glass was satisfactory andbubbles were hardly generated. Thus, when the oxide of the rare earthelement is contained in an amount of more than 2.9% by weight, theflowability and the deaeration of the glass are damaged due to increasein the tendency of crystallization and the resulting glass is notpreferred as a sealing glass.

FIG. 3 shows the relation between deformation temperature and content ofthe oxide of rare earth element in the glasses A-D which gave goodresults in preparation of the glass and in making the structure in Table5, and FIG. 4 shows the relation between the micro Vickers hardness andthe content. In FIG. 3 and FIG. 4, ∘, Δ and □ show the characteristicsof glasses containing Pr, Nd and Er, respectively.  is a plot of theglass No.1 containing no lanthanide element.

                                      TABLE 5                                     __________________________________________________________________________    No.   6A 6B  6C 6D 6E 6F 7A 7B  7C 7D 7E 7F  14A                                                                              14B                                                                              14C                                                                              14D                                                                              14E                                                                              14F               __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55 55                     SiO.sub.2 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20 20                                                                          B.sub.2                                                                      O.sub.3 8 8 8                                                                 8 8 8 8 8 8 8                                                                 8 8 8 8 8 8 8                                                                 8                   Al.sub.2 O.sub.3 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2                          ZnO 6.9 6.7 5 4.1 4 3 6.9 6.7 5 4.1 4 3 6.9 6.7 5 4.1 4 3                     Na.sub.2 O 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8 8                                Ln.sub.2 O.sub.3 0.1 0.3 2 2.9 3 4 0.1 0.3 2 2.9 3 4 0.1 0.3 2 2.9 3 4                                                                   Ln Pr Pr Pr                                                                  Pr Pr Pr Nd                                                                   Nd Nd Nd Nd                                                                   Nd Er Er Er                                                                   Er Er Er                                                                       Tg (°                                                                 C.) 380 378                                                                   378 385 387                                                                   -- 383 378                                                                    378 383 385                                                                   -- 380 377                                                                    380 380 382                                                                   --                  Td (° C.) 422 422 425 433 435 -- 423 427 422 428 430 -- 424 428                                                                  428 429 431                                                                   --                  Hv 399 447 450 441 443 -- 401 427 423 435 437 -- 397 430 452 433 435 --       Vitrification ◯  ◯  ◯  ◯                                                                 ◯                                                                 X .largecircl                                                                e.  .largecirc                                                                le.  .largecir                                                                cle.                                                                          ◯                                                                  ◯                                                                 X .largecircl                                                                e.  .largecirc                                                                le.  .largecir                                                                cle.                                                                          ◯                                                                  ◯                                                                 X                Structure                                                                           ◯                                                                    ◯                                                                     ◯                                                                    ◯                                                                    Bubbles                                                                             ◯                                                                    ◯                                                                     ◯                                                                    ◯                                                                    Bubbles                                                                              ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    Bubbles              __________________________________________________________________________

As shown in FIG. 3, the deformation temperature was about 420° C. andshowed substantially no change with change of the content of theelement. Moreover, as shown in FIG. 4, the micro Vickers hardness wasmaximum when content of the oxide of every element was 1.0% by weight(Nos. 6, 7 and 14). When the content exceeded 1.0% by weight, the microVickers hardness was about 440, which was higher than that of the glassNo. 1, but the hardness decreased with increase of the content. Further,for all of the elements, when the content of the oxide was 0.3% byweight, the micro Vickers hardness sharply increased to higher than 420,but when it was 0.1% by weight (Nos. 6A, 7A and 14A), the hardness wasabout 400 and, thus, the effect of the addition was small.

In order to elucidate the causes therefor, glasses changed in thecontent of the rare earth elements were observed by a transmission typeelectron microscope to examine the relation between the content of therare earth element and the particle size of the precipitated fineparticles. FIG. 5 shows the relation between the amount of Er oxide whenEr was contained as the rare earth element and the particle size of thefine particles. The particle size of the precipitated particlesincreased with increase in the amount of the Er oxide added, and whenthe amount was 2.0% by weight, the particle size was about 20 nm andwhen 2.9% by weight, it was about 50 nm. In this case, the flowabilityof the glass was not damaged. When the amount was 3.0% by weight, theparticle size was more than 50 nm. When the particles size reached suchdegree, the flowability of the glass was damaged. Therefore, when theparticle size of the fine particles present in the glass is 50 nm orless, the flowability of the glass is not damaged and this glass iseffective as a sealing glass.

Furthermore, when the content of the Er oxide was 0.3% by weight, theparticle size was 1 nm and when 0.1% by weight, the particle size wasless than 1 nm. FIG. 6 shows the relation between the particle size andthe micro Vickers hardness. As in FIG. 6, when the particle size was 1nm, the micro Vickers hardness was improved, but when the particle sizewas less than l nm, the micro Vickers hardness showed substantially nochange. Moreover, when the particle size was about 3 nm to 10 nm, themicro Vickers hardness could be increased to about 460. When theparticle size was less than 3 nm and more than 10 nm, the increase ofthe micro Vickers hardness was small.

From the above, when the particle size of the precipitated fineparticles is 1-50 nm, the micro Vickers hardness of glass is improvedand the flowability of the glass is not damaged, and, thus, asatisfactory glass can be obtained. That is, when particle size of thefine particles is less than 1 nm, improvement of the micro Vickershardness is small, and when it exceeds 50 nm, flowability of the glassdecreases and deaeartion is also inferior. Further, when the particlesize of fine particles is 3-10 nm, the increase of micro Vickershardness is great.

From the viewpoint of the content of oxides of the rare earth elements,when it exceeds 2.9% by weight, flowability and deaeration of the glassare both inferior. When it is less than 0.3% by weight, the increase ofmicro Vickers hardness is small. Therefore, content of the oxides of therare earth elements, is preferably 0.3-2.9% by weight. More preferably,when it is 0.5-1.5% by weight, the increase of micro Vickers hardness isgreat.

In the above, boron oxide and silicon oxide were used as oxides forforming network of glass, but in addition, glasses containing phosphorusoxide or fluorine can be considered to be components of low-temperaturebonding glass. When glass was prepared using them as components, a glasscontaining rare earth element was obtained, but no improvement inmechanical strength resulting from addition of the rare earth elementswas seen. It is considered that this is because the solubility of therare earth elements in the glass is high and no crystallites having therare earth elements as nuclei are produced. From this fact, it ispreferred to use boron oxide and/or silicon oxide as the network-formingoxides for glass.

Furthermore, the structures made in this Example were very high inreliability because they were sealed using the glass of the presentinvention which had a high strength and contained few bubbles.

EXAMPLE 3

In this Example, investigation was made on the compositional ranges ofthe respective components of a glass which could be stably obtained andimproved in mechanical strength by containing oxides of rare earthelements.

Tables 6-9 show the blending compositions (% by weight), state ofvitrification, transparency, quality of the resulting structures, glasstransition temperature (Tg/° C.) and deformation temperature (Td/° C.)obtained from thermal expansion characteristics, and micro Vickershardness (Hv) of the investigated glasses. In Tables 6 and 7, theglasses of Nos. 22-50 corresponded to those of Nos. 51-82 shown inTables 8 and 9 containing heavy metal oxides such as PbO, Bi₂ O₃, etc.,to which 1.0% by weight of Er₂ O₃ was additionally contained.

                                      TABLE 6                                     __________________________________________________________________________    No.   22 23 24 25 26  27 28 29 30 31 32 33 34 35 36                           __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 83 78 52 40 65 34 69 55 91 56 90 84 55 44 77                              SiO.sub.2  4  4 20 20 12 12  9  8  2 30  1  3  5 26  4                        B.sub.2 O.sub.3 12 12  6  8  7  8 13 22  6 10  6  7 14  8 13                  Al.sub.2 O.sub.3 --  4  2  2  4 --  5  2 --  1 --  3  6  3  4                 ZnO --  1  9  6 -- -- --  6 -- --  2  3  8  8  1                              Na.sub.2 O -- --  5  8  1 --  2  6 --  2 --  3  5  6 --                       K.sub.2 O -- --  5 -- -- -- -- -- -- -- -- --  6  4 --                        Bi.sub.2 O.sub.3 -- -- -- 15 -- 45 -- -- -- -- -- -- -- -- --                 TeO.sub.2 -- -- -- -- 10 -- -- -- -- -- -- -- -- -- --                        Fe.sub.2 O.sub.3 -- -- -- -- -- --  1 -- -- -- -- -- -- --                    Er.sub.2 O.sub.3  1  1  1  1  1  1  1  1  1  1  1  1  1  1  1                 Vitrification ◯ ◯ ◯ ◯                                                        ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e.                             Trans- ◯ ◯ ◯ X ◯ X X                                                         ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e.                             parency                                                                       Structure ◯ ◯ ◯ ◯                                                            Bubbles ◯                                                         ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                               Tg (° C.) 330                                                         352  370  372  387  413                                                       388  367  302  405  295                                                       341  354  480  360                                                             Td (° C.) 369                                                         391  417  426  425  436                                                       425  401  340  508  333                                                       372  402  530  402                                                             HV 340  365  440  465                                                        426  481  430  379  322                                                       516  302  342  405  548                                                       403                          __________________________________________________________________________

                                      TABLE 7                                     __________________________________________________________________________    No.   37 38 39 40 41 42 43 44 45 46 47 48 49 50                               __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 55 50 65 50 50 51 92 60 59 69 45 45 43 71                                 SiO.sub.2 10 25 12 26 16 15  1 32 28 25 17 17 27 21                           B.sub.2 O.sub.3 20  9  8  8 19 19  6  7 13  5  7  7  8  4                     Al.sub.2 O.sub.3  2  3  5  2  2  2 -- -- -- --  8  8  3 --                    ZnO  6  3  5  8  8  8 -- -- -- -- 10 10  8 --                                 Na.sub.2 O  6  9  4  5  4  4 -- -- -- -- 12  6  6  3                          K.sub.2 O -- -- -- -- -- -- -- -- -- -- --  6  4 --                           Bi.sub.2 O.sub.3 -- -- -- -- -- -- -- -- -- -- -- -- -- --                    TeO.sub.2 -- -- -- -- -- -- -- -- -- -- -- -- -- --                           Fe.sub.2 O.sub.3 -- -- -- -- -- -- -- -- -- -- -- -- -- --                    Er.sub.2 O.sub.3  1  1  1  1  1  1  1  1  1  1  1  1  1  1                    Vitrification ◯ ◯ ◯ ◯                                                    ◯ ◯                                                   X X X X X X X X                    Trans- ◯ ◯ ◯ ◯ .largecir                                                 cle. ◯ X X X X X                                                  X X X                              parency                                                                       Structure ◯ ◯ ◯ ◯                                                        ◯ ◯                                                   X X X X X X X X                    Tg (° C.) 372  415  384  471  440  432  -- -- -- -- -- -- -- --                                                    Td (° C.) 411  468                                                    422  501  486  474  -- -- --                                                  -- -- -- -- --                     Hv 443  512  425  526  502  480  -- -- -- -- -- -- -- --                    __________________________________________________________________________

                                      TABLE 8                                     __________________________________________________________________________    No.   51 52 53 54 55  56 57 58 59 60 61 62 63 64 65                           __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 84 78 52 40 66 35 70 56 92 57 90 84 55 44 77                              SiO.sub.2  4  4 20 20 12 12  9  8  2 30  1  1  5 26  4                        B.sub.2 O.sub.3 12 12  6  8  7  8 13 22  6 10  6  5 14  8 13                  Al.sub.2 O.sub.3 --  4  2  2  4 --  5  2 --  1 --  3  6  3  4                 ZnO --  2 10  7 -- -- --  6 -- --  3  4  9  9  2                              Na.sub.2 O -- --  5  8  1 --  2  6 --  2 --  3  5  6 --                       K.sub.2 O -- --  5 -- -- -- -- -- -- -- -- --  6  4 --                        Bi.sub.2 O.sub.3 -- -- -- 15 -- 45 -- -- -- -- -- -- -- -- --                 TeO.sub.2 -- -- -- -- 10 -- -- -- -- -- -- -- -- -- --                        Fe.sub.2 O.sub.3 -- -- -- -- -- --  1 -- -- -- -- -- -- -- --                 Er.sub.2 O.sub.3 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --                 Vitrification ◯ ◯ ◯ ◯                                                        ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e.                             Trans- ◯ ◯ ◯ X ◯ X X                                                         ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e.                             parency                                                                       Structure ◯ ◯ ◯ ◯                                                            Bubbles ◯                                                         ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                              ◯ .largecircl                                                     e. ◯                                                               Tg (° C.) 328                                                         351  370  372  385  412                                                       389  365  306  402  293                                                       340  352  480  360                                                             Td (° C.) 367                                                         390  417  423  427  440                                                       427  398  343  510  330                                                       373  400  530  402                                                             Hv 330  338  381  401                                                        381  420  401  362  296                                                       435  275  332  370  514                                                       351                          __________________________________________________________________________

                                      TABLE 9                                     __________________________________________________________________________    No.   66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82                      __________________________________________________________________________    Composition                                                                     % by weight                                                                   PbO 55 50 65 50 50 51 93 53 60 70 45 45 43 72 61 62 55                        SiO.sub.2 10 25 12 26 16 15  1 32 28 25 17 17 27 21  3  3  5                  B.sub.2 O.sub.3 20  9  8  8 19 19  6 15 12  5  7  7  8  4 11 11 12                                                                 Al.sub.2 O.sub.3                                                             2  3  5  2  2  2 --                                                           -- -- --  8  8  3                                                             --  7  5  7                                                                    ZnO  7  4  6  9  9                                                            9 -- -- -- -- 11                                                             11  9 -- 11  9  8                                                              Na.sub.2 O  6  9                                                             4  5  4  4 -- -- --                                                           -- 12  6  6  3  4                                                             3  8                      K.sub.2 O -- -- -- -- -- -- -- -- -- -- --  6  4 -- -- --  4                  Bi.sub.2 O.sub.3 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --                                                                TeO.sub.2 -- -- --                                                           -- -- -- -- -- --                                                             -- -- -- -- -- --                                                             -- --                     Fe.sub.2 O.sub.3 -- --  -- -- --  --  -- -- -- --  --  --                     Er.sub.2 O.sub.3 -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --                                                                SrO -- -- -- -- --                                                           -- -- -- -- -- --                                                             -- -- --  3 -- --                                                              BaO -- -- -- -- --                                                           -- -- -- -- -- --                                                             -- -- -- --  7 --                                                              TiO.sub.2 -- -- --                                                           -- -- -- -- -- --                                                             -- -- -- -- -- --                                                             --  1                     Vitrification ◯ ◯ ◯ ◯                                                             ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯ X X X       Trans- ◯ ◯ ◯ ◯ .largecir                                                          cle. ◯                                                            ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯                                                                 ◯ X X X       parency                                                                     Structure                                                                           ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    ◯                                                                    Bubbles                       Tg (° C.)                                                                    375                                                                              413                                                                              384                                                                              475                                                                              440                                                                              432                                                                              298                                                                              475                                                                              460                                                                              410                                                                              420                                                                              415                                                                              468                                                                              385                                                                              342                                                                              332                                                                              335                       Td (° C.) 412  468  422  509  486  474  335  519  481  432  442                                                            439  506  419  367                                                            357  365                  Hv 375  450  396  462  410  421  280  422  462  416  420  418  430  352                                                            420  400  420          __________________________________________________________________________

In Tables 6-9, the respective evaluations were conducted in the samemanner as in Example 1. The heat treating temperature in making thestructures was a temperature at which viscosity of the glass reached 104poises and they were kept at that temperature for 30 minutes. Theatmosphere was under vacuum. The transparency was evaluated by examininglight transmission for visible light of a test piece of about 10 mmthick cut out from the glass block.

As shown in Tables 8-9, the glasses of Nos. 51-79 containing no oxidesof rare earth elements all vitrified.

No. 35 in Table 6 containing 44% by weight of PbO vitrified, but No. 49in Table 7 containing 43% by weight of PbO did not vitrify. No. 43 inTable 7 containing 92% by weight of PbO did not vitrify, but No. 30containing 91% by weight of PbO and No. 32 containing 90% by weight ofPbO in Table 6 vitrified. Therefore, content of PbO is preferably 44-91%by weight.

As for Nos.46 and 50 in Table 7, since the content of B₂ O₃ was 5% byweight and 4% by weight, Er₂ O₃ powder added remained in the form of thepowder in the glass and could not be uniformly dispersed in the glassstructure. In Nos. 24, 30 and 32 in Table 6, the content of B₂ O₃ was 6%by weight, but the Er₂ O₃ powder was uniformly dissolved in the glass.Therefore, the content of B₂ O₃ is preferably 6% by weight or more.

In No. 44 in Table 7, the content of SiO₂ was 32% by weight, but Er₂ O₃powder remained in the glass and could not be uniformly dispersed in theglass structure. In No.31 in Table 6, since the content of SiO₂ was 30%by weight, the Er₂ O₃ powder could be uniformly dispersed. Therefore,the content of SiO₂ is preferably 30% by weight or less.

In No. 45 in Table 7, the content of SiO₂ was less than 30% by weightand the content of B₂ O₃ was 6% by weight or more, but since the totalcontent of SiO₂ and B₂ O₃ was 41% by weight, the sample was outside thevitrification region and did not vitrify. On the other hand, in No. 31in Table 6, since the total content of SiO₂ and B₂ O₃ was 40% by weight,it was within the vitrification region and vitrified. When the totalcontent of SiO₂ and B₂ O₃ is less than 6% by weight, the added Er₂ O₃powders remained as they were in the glass and this is not preferred.Therefore, it is preferred that the total content of SiO₂ and B₂ O₃ is6-40% by weight.

Next, when attention is given to the micro Vickers hardness of theglass, among the above glasses, those which vitrified all increased inthe micro Vickers hardness. No. 22 and No. 23 in Table 6 had the PbOcontents of 83% by weight and 78% by weight, respectively and were smallin the degree of increase of the micro Vickers hardness. On the otherhand, No. 36 in Table 6 had the PbO content of 77% by weight, butgreatly increased in the micro Vickers hardness. Accordingly, the PbOcontent is preferably 77% by weight or less.

No. 29 in Table 6 contained 22% by weight of B₂ O₃ and was small inincrease of the micro Vickers hardness. However, No. 37 in Table 7contained 20% by weight of B₂ O₃ and markedly increased in the microVickers hardness. Therefore, the B₂ O₃ content is more preferably 20% byweight or less.

When oxides such as Al₂ O₃, ZnO, etc. are contained, the micro Vickershardness can be improved, but No. 47 and No. 48 in Table 7 did notvitrify because the total content of Al₂ O₃, ZnO and R₂ O (R: an alkalimetal element) was 30% by weight, irrespective of the kind of the alkalimetal oxide. In No. 34 in Table 6, the total content of Al₂ O₃, ZnO andR₂ O (R: an alkali metal element) was 25% by weight and in No.35 thetotal content was 21% by weight, and they vitrified. Therefore, thetotal content of Al₂ O₃, ZnO and R₂ O (R: an alkali metal element) ispreferably 25% by weight or less.

In No. 25 and No. 27 in Table 6, a part of PbO was replaced with Bi₂ O₃which is one of heavy metal oxides. These glasses were greatly improvedin the micro Vickers hardness due to containing of an oxide of Er.However, since they deeply colored, it was difficult to find cracks orbubbles inside the glass. Therefore, it is not preferred to use theseglasses as sealing glass. As the oxides which cause coloration of glass,there are additionally Sb₂ O₃, Fe₂ O₃, etc. For this reason, No. 28 wasalso not preferred as a sealing glass.

Furthermore, the glass of No. 26 which contained TeO₂ was greatlyimproved in the micro Vickers hardness due to the addition of Er oxideand was superior in transparency. However, upon making a structure usingit and examining the generation of bubbles, there were many bubbles inthe glass and, thus, this was not preferred as a sealing glass.

From the above, the heavy metal oxide is more preferably an oxide oflead.

No. 80 and No. 81 in Table 9 did not vitrify at the time of preparingthe glass. Therefore, these glasses are not preferred as sealing glass.Furthermore, when structures were made using these glasses andadditionally No. 82, the glasses lost flowability and the grooves of thesubstrate in FIG. 8 were not filled with the glasses. Therefore, theseglasses are difficult to use as sealing glasses.

Observation of the glasses prepared in the above Examples by atransmission type electron microscope showed that there were presentfine particles of several nm to several ten nm though the particle sizevaries depending on the glasses. It is considered that the micro Vickershardness increased due to the presence of these fine particles.

From the above Examples 2 and 3, it can be seen that a satisfactoryglass can be obtained when it comprises, in terms of the followingoxides, PbO: 44-91% by weight, B₂ O₃ : 6% by weight or more, SiO₂ :0-30% by weight, the total of SiO₂ and B₂ O₃ : 6-40% by weight, and Ln₂O₃ (Ln: Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); 0.3-2.9% byweight and when fine particles are uniformly dispersed in the glass.

More preferably, the mechanical strength can be remarkably improved whenit comprises PbO: 44-77% by weight, B₂ O₃ : 6-20% by weight, SiO₂ :0-30% by weight, at least one of ZnO, Al₂ O₃ and R₂ O (R: an alkalimetal element): 0-25% by weight and Ln₂ O₃ (Ln: Y. Pr, Nd, Sm, Eu, Gd,Tb, Dy, Ho, Er, Tm, Yb, Lu): 0.5-1.5% by weight and when fine particlesare uniformly dispersed in the glass.

EXAMPLE 4

Table 10 shows amount of the filler added to the sealing glass preparedby mixing various low-expansion filler powders with the glass of No. 14in Table 1, particle size of the filler, and thermal expansioncoefficient (α, 50-300° C.), transition temperature (Tg/° C.) anddeformation temperature (Td/° C.) obtained from thermal expansioncharacteristics, and micro Vickers hardness (Hv) of the glass. ZrSiO₄,PbTiO₃, β-eucryptite and silica glass were used as the fillers. Theamount and particle size of the fillers were those which were the mostpreferred for each of the fillers.

                                      TABLE 10                                    __________________________________________________________________________                    Particle                                                           Amount size α(×10.sup.-7 /° C.) Tg Td                   No. Glass Filler (Vol %) (μm) (50˜300° C.) (°                                          C.) (° C.) Hv                        __________________________________________________________________________    83 14 ZrSiO.sub.3                                                                         44  15.0                                                                              72.6    382                                                                              421                                                                              465                                           84  PbTiO.sub.3 10 6.2 64.7 375 414 460                                       85  β- 21 25.0 52.3 381 420 471                                            eucryptite                                                                  86  Silica 15 4.5 69.4 386 425 472                                              glass                                                                       14  -- -- -- 116.8 379 418 462                                              __________________________________________________________________________

This sealing glass was prepared in the following manner. A block of theglass No. 14 was ground by a mill to make powders. Then, thelow-expansion filler powder was added thereto, followed by wet mixingusing acetone. Thereafter, the mixture was molded into pellets of about40 mm+, which were heated at 500° C. to sinter the glass powder and thelow-expansion filler powder to obtain a block of the sealing glass. Testpieces for thermal expansion characteristics and micro Vickers hardnesswere cut out from this block and subjected to the tests.

As shown in Table 10, the thermal expansion coefficient of the glass No.14 containing no low-expansion filler was about 117×10⁻⁷ /° C. whilethat of the sealing glasses of Nos.83-86 containing the low-expansionfillers was 52-72×10⁻⁷ /° C. The glass transition temperature and thedeformation temperature somewhat differed from those of the glass No.14. This is because Zr, Si, etc. which were components of the fillerswere taken into the glass structure owing to the reaction which tookplace by heating after addition of the fillers. Moreover, the microVickers hardness was very high, namely, about 470.

As mentioned above, bond portions of high reliability can be obtainedeven for the materials of low thermal expansion coefficient by using asealing glass prepared by adding a low-expansion filler to a glass whichcontains a rare earth element and in which fine particles are unifromlydispersed. Furthermore, from Example 1, the rare earth elements to beadded are preferably one or more of Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb and Lu.

Furthermore, from the investigation in Example 2, the particle size ofthe fine particles present in the glass is preferably 1-50 nm. It isfurther preferred that the glass contains an oxide of lead and boronoxide and/or silicon oxide. Moreover, the low-expansion fillers used arepreferably one or more of zirconium silicate, lead titanate,β-eucryptite and silica glass.

FIG. 12 is a graph which shows the relation between the amount of PbOand the amount of SiO₂ +B₂ O₃ in Examples 1-4. The amount of PbO andthat of SiO₂ +B₂ O₃ in these Examples are in the area surrounded by theline drawn linking point a (30%, 18%), point b (50%, 50%), point c (94%,6%), point d (80%, 6%), point e (65%,. 18%) and the point a, and in thisarea, the Vickers hardness can be 370 or higher and the deformationtemperature can be 500° C. or lower.

FIG. 13 shows the relation between the amount of SiO₂ +B₂ O₃ and theVickers hardness. As shown in this figure, the hardness increases withincrease of the amount of SiO₂ +B₂ O₃. The white dot indicates theternary system of PbO--SiO₂ --B₂ O₃ and the black dot indicates theabove ternary system which additionally contains other componentsexcluding the rare earth elements. As shown in this figure, some of theglasses containing Al₂ O₃, ZnO, Na₂ O, K₂ O, Bi₂ O₃, TeO₂, Pe₂ O₃ inaddition to SiO₂ +B₂ O₃ increase in the hardness and others decrease inthe hardness than the ternary system. These components are organicallyrelated with each other and glasses of the desired hardness anddeformation temperature can be obtained by the mutual combinations.

The solid line in the figure can be obtained by linking the points of(SiO₂ +B₂ O₃ 8%, Hv 290), (SiO₂ +B₂ O₃ 40%, Hv 462), and (SiO₂ +B₂ O₃47%, Hv 422) from the relation between the amount of SiO₂ +B₂ O₃ and thehardness. The especially preferred hardness Hv is a hardness higher thanthe value obtained from the formula 242+5.5×[SiO₂ (%)+B₂ O₃ (%)]. Thehardness Hv of the dotted line is preferably higher than the valueobtained from the formula 230+5.23×[SiO₂ (%)+B₂ O₃ (%)].

FIG. 14 shows the relation between the Vickers hardness and thedeformation temperature. As shown in this figure, the hardness increaseswith increase of the deformation temperature. The white dot indicatesthe ternary system containing SiO₂ +B₂ O₃ and this ternary system whichadditionally contains other components excluding the rare earthelements, and the line is of the ternary system. The black dot indicatesthe glass containing rare earth elements, and higher hardness isobtained at the same deformation temperature than those of the ternarysystem. It is considered that this is because fine precipitate wasproduced with the rare earth elements. The solid line in the figure canbe obtained by linking the points of (Td 330° C., Hv 260), (Td 432° C.,Hv 416), (Td 481° C., Hv 462), and (Td 519° C., Hv 422) from therelation between the hardness and the deformation temperature. Theespecially preferred are those having a hardness above the solid line.The hardness of the glass of the dotted line is obtained from theformula -102+1.087×Td(° C.) and preferred are those having a hardnesshigher than the value obtained from the formula.

EXAMPLE 5

Evaluation was carried out with respect to other utilization field ofglass. Table 11 shows compositions of glass evaluated. No. 87 is aborasilicate glass, No. 88 is a pannel glass for a cathode-ray tube, andNo. 89 is a soda-lime glass. The borosilicate glass is used for heatresistant materials such as a Pyrex glass, a glass pannel for a liquidcrystal display, and the like. The soda-lime glass is used for a plateglass, a pannel glass for a plasma display, and the like. To these typesof glass, one of rare earth metal oxides, i.e., Er₂ O₃ is added in theamount shown in Table 11. For reference, Hv of each of the glass beforeadding Er₂ O₃ is also shown in Table 11. As seem from this table, Hv ofeach of the glass was considerably enhanced by adding the rare earthmetal oxide. By the observation of these glass materials containing therare earth metal oxide by a transmission electron microscope, fineparticles having particle diameter of about 10 nm were found. Thus, theadvantageous effect of the present invention can be attained in the caseof the borosilicate glass, soda- lime glass, and the like.

                                      TABLE 11                                    __________________________________________________________________________                                    Hv     Hv                                       Composition (wt %) (before adding (after adding                             No.                                                                              SiO.sub.2                                                                        B.sub.2 O.sub.3                                                                  Na.sub.2 O                                                                       Al.sub.2 O.sub.3                                                                  CaO                                                                              MgO                                                                              BaO                                                                              PbO                                                                              Er.sub.2 O.sub.3                                                                  Er.sub.2 O.sub.3)                                                                    Er.sub.2 O.sub.3)                      __________________________________________________________________________    87 80.9                                                                             12.8                                                                             4.0                                                                              2.3 -- -- -- -- 5.0 620    702                                      88 62.4 -- 15.9 3.7 1.8 1.1 12.5 2.6 13.0 522 599                             89 72.5 -- 14.0 1.4 8.0 4.1 -- -- 10.0 615 683                              __________________________________________________________________________

EXAMPLE 6

This Example shows a structure constructed by bonding two materialsusing a low-temperature sealing glass. As the materials to-be bondedflat plates of Mn--Zn ferrite single crystal were used. The glass of No.14 was used as the sealing glass. As comparative examples, the similarstructures were made using the glass of No. 79 in Table 7 having thenearly the same deformation temperature as the glass of No.14 and aZnO--B₂ O₃ --SiO₂ --Na₂ O--BaO glass (A) having a deformationtemperature higher 100° C. than that of the glass No. 14. The glass (A)is high in deformation temperature and high in mechanical strength, and,hence, is used for bonding of materials high in heat resistance.

The structure was made by sandwiching the sealing glass plate somewhatsmaller in size than the ferrite plate between two ferrite singlecrystal flat plates of 20 mm long, 15 mm wide and 1 mm thick and heattreating them under application of a load to obtain a bonded structure.The heat treating was carried out at 580° C. for 30 minutes under vacuumfor the glasses of Nos.14 and 79, and at 750° C. for 10 minutes undervacuum for the glass (A). The resulting bonded structures were cut to 2mm wide, 1 mm long and 2.2 mm thick.

Bond strength of the bonded portion of the structures was measured. FIG.9 is an oblique view which shows the measuring method. The test piececut out was set on the three-point bending strength measuring jigs 4, 4'so that the bonded face of the test piece was perpendicular to theground and parallel with the longer direction of the three-pointstrength measuring jigs. The span n between 4 and 4' was 1.2 mm. Aftersetting the sample, a load w was applied to the test piece by loadingjig 3, and the maximum stress was taken to be a breaking load andbreaking stress σ was calculated by the following formula. ##EQU1##wherein a is the width of the test piece and t is the thickness of theglass.

                  TABLE 12                                                        ______________________________________                                               The                                                                       number of  Made of                                                           No. measurement σ(MPa) breaking Note                                  ______________________________________                                        14     40        100        Ferite Example                                      79 42 80 Glass, Comparative                                                      interface Example                                                          (A) 41 90 Ferrite Comparative                                                     Example                                                                 ______________________________________                                    

The average breaking stress a and breaking mode of the structures bondedusing the respective glasses are shown in Table 12. As shown in thistable, the breaking stress of the structure made using the glass No. 14and that of the structure made using the glass No. 79 were 100 MPa and80 MPa, respectively, and the breaking stress of the former was higher20% than that of the latter. The breaking stress of the structure madeusing the glass (A) was 90 MPa. Thus, the structure made using the glassNo. 14 showed the higher breaking stress.

The mode of breaking of the test piece was observed to find that thebreaking occurred at the bonding interface or the glass part in thestructure made using the glass No.79 while the breaking occurred at theferrite substrate in most of the test pieces of the structures madeusing the glass No.14 and the glass (A). Thus, the structure made usingthe glass of the present invention had a mechanical strength equal to orhigher than the structure bonded at a high temperature using the glassof high deformation temperature in spite of the fact that the bondingtemperature was low. Thus, high reliability of the bonded part could beattained in the structure of the present invention.

As shown above, the structure of the present invention had a bondportion very high in reliability. That is, the reliability of the glassper se is high by using a glass capable of bonding at low temperaturesand high in mechanical strength as shown in Example 1. Further, sincethis glass generates few bubbles and intimately bonds to the material tobe bonded, breaking at the bonding interface hardly occurs.

EXAMPLE 7

The same structure as of FIG. 7 and Exampl 6 was made using the sealingglass of No. 84 in Table 10. A sintered α-alumina having a thermalexpansion coefficient of 70×10^(-7/) ° C. was used as the substrate andthe material to be bonded. The bonding conditions were the same as inExamples 1 and 6. Neither bubbles nor cracks were seen and wettabilityto the substrate and the material to be bonded was satisfactory.Moreover, a structure having a satisfactory bond strength and a glassbonding part high in reliability was obtained.

EXAMPLE 8

Magnetic heads were made using the sealing glasses of the presentinvention shown in Examples 1-4. FIG. 15 and FIG. 16 are oblique viewsof a magnetic head made in accordance with the present invention. FIG.15 shows so-called ferrite head using Mn--Zn ferrite single crystal.FIG. 16 shows a magnetic head made by forming a magnetic film bysputtering using the Mn--Zn ferrite single crystal as a support. Thereference numerals 11, 11' indicate magnetic cores, 12 indicates a coilwinding window, 14 indicates a magnetic film, 15 indicates a magneticgap, and 16 indicates a sealing glass. The symbol t indicates a slidingwidth, T indicates a core width which was about 0.15 mm, C' indicates acore thickness which was about 2.3 mm, H indicates a height of the headwhich was about 1.7 mm, and the core width t of sliding part was about0.14 mm. In this Example, an Fe--Ta--C magnetic film (saturated magneticflux density Bs=12000 gausses) was used as the magnetic film 14. Themagnetic head shown in FIG. 16 is hereinafter referred to as FTC head.

FIGS. 17-19 show a method for making the magnetic head of the presentinvention. As shown in FIG. 17, a coil winding groove 12 and trackgrooves 13 were cut in a substrate which was magnetic core 11, therebyto form a magnetic gap face. Then, as shown in FIG. 18, the Fe--Ta--Cmagnetic film 14 of about 5 μm was formed on the magnetic gap face byhigh frequency sputtering method. Furthermore, an SiO₂ layer 15 of about0.15 μm as a gap spacer was formed by high frequency sputtering methodon the magnetic core 11 as a substrate or on the magnetic film 14. Inaddition, Cr film 17 of about 0.10 gm was formed as a reactioninhibiting film for inhibition of reaction with the sealing glass.

Next, as shown in FIG. 19, magnetic cores 11 and 11' as substrates onwhich the magnetic film as the magnetic core was formed were butted toeach other from left and right, and sealing glass rod 16 was placed andheated to a temperature at which the viscosity of the glass reached 10⁴poises in a vacuum and the assembly was maintained for 25 minutes tobond the left and right core blocks. When cooled at a rate of 1-2°C./min, the assembly was kept at a temperature lower about 70° C. thanthe sealing temperature for 20 minutes. Then, the assembly was subjectedto abrasion, grinding and cutting to obtain an FTC head shown in FIG.16. The ferrite head shown in FIG. 15 was made in the same manner asabove, except for omitting the step of forming the Fe--Ta--C magneticfilm 14 and the reaction inhibiting film 17 on the magnetic gap face.

Next, the sealing glass used for bonding will be studied. Since theFe--Ta--C magnetic film has a saturated magnetic flux density of 1.3-1.5tesla, but is low in resisting temperature, namely, 600° C., the bondingstep with glass must be carried out at lower than that temperature.Therefore, the galsses of Nos. 31 and 35 in Table 6 and Nos. 38, 40, 41,and 42 in Table 7 which have a deformation temperature of 450° C. orhigher are difficult to carry out the bonding at lower than 600° C.Thus, they are not preferred as sealing glass for magnetic heads havingthe Fe--Ta--C magnetic film.

That is, the total content of network forming oxide components such asB₂ O₃ and SiO₂ in these glasses is about 35% by weight and, so, are highin characteristic temperature. The total content of B₂ O₃ and SiO₂ inthe glass No. 37 in Table 7 is 30% by weight, but its deformationtemperature is low, namely, 411° C., and, therefore, the bondingtemperature can be lower than 600° C. Thus, the total content of B₂ O₃and SiO₂ is desirably 30% by weight or less. Moreover, from Example 3,the content of PbO is preferably 44-77% by weight. Further, the contentof B₂ O₃ is preferably 6-20% by weight and that of SiO₂ is preferably30% by weight or less. When the glass contains Al₂ O₃, ZnO and R₂ O (R:an alkali metal element), a magnetic head having glass bonding part ofhigh reliability can be obtained.

For the above reasons, glasses Nos. 10, 14, 6B, 34, 37 and 39 wereselected as the sealing glass and FTC heads were made. As comparativeexamples, FTC heads were similarly made selecting glasses of No. 55 andNo. 79 from Tables 8 and 9. Further, a ferrite head was also made usingthe glass of No. 14. No. of the sealing glass, bonding temperature,production yield (%), head chip strength (gf), head performances andhead breaking time in sliding test conducted at a relative speed withmagnetic recording medium of 11, 20 and 52 m/sec are shown in Table 13.A metal tape or metal deposited tape having a coercive force of at least1000 Oe, preferably at least 1500 Oe was used as the magnetic recordingmedium.

The head chip strength was measured by the tensile test method shown inFIG. 20. In FIG. 20, 29, 29' indicate fixing jigs for head chip, 30indicates a folding resistance tester, 31 indicates a folding resistancetester installing stand, and 32 indicates a head chip. The headperformance was determined by winding five head chips with coils andevaluating the magnetic characteristics thereof. The samples having goodresults are shown by "∘" and those having problems are shown by "Δ".With reference to the head breaking time in the sliding test, the headchips which broke in more than 500 hours are shown by "⊚", and when thehead chip broke in less than 500 hours, the time required for breakingis mentioned. The sliding width t of the magnetic head was 65 μm, thecore width T was 207 μm, the core thickness C' was 1.52 mm and theheight H of the head was 1.9 mm.

                                      TABLE 13                                    __________________________________________________________________________                               Head breaking time (hr)                                    Bonding  Chip      Relative                                                                           Relative                                                                           Relative                                    temperature Yield strength Head speed speed speed                            No. (° C.) (%) (gf) performance 11 (m/sec) 20 (m/sec) 52             __________________________________________________________________________                                         (m/sec)                                  FTC head                                                                           10 580   96 402 ◯                                                                       ⊚                                                                   ⊚                                                                   ⊚                            14 580 94 386 ◯ ⊚ ⊚ .circlein                                         circle.                                     6B 580 89 271 ◯ ⊚ ⊚ .circlein                                         circle.                                     34 540 64 254 ◯ 314 209 120                                       37 560 90 323 ◯ ⊚ ⊚ .circlein                                         circle.                                     39 590 90 311 ◯ ⊚ ⊚ .circlein                                         circle.                                     55 580 56 250 ◯ ⊚ 394 245                          79 560 62 210 ◯ 493 336 216                                      Ferrite 14 580 94 400 Δ ⊚ ⊚                                                  ⊚                         __________________________________________________________________________

The head chips prepared by bonding with the glasses of Nos. 10, 14, 37and 39 had a yield of more than 90% and a chip strength of higher than300 g, and had a high reliability. Furthermore, these head chips did notbreak for more than 500 hours in the sliding test of 52 m/sec inrelative speed. On the other hand, in the case of using the glasses ofNo. 6B and 34, the head chips were higher in the yield and the strengththan those prepared by bonding with the comparative glasses of Nos. 55and 79, but were less than 90% in the yield and lower than 300 g in thechip strength. Besides, the results of the sliding test were less than500 hours under some conditions, and these heads can hardly be said tohave high reliability.

It is considered that this is because micro Vickers hardness of glassesof Nos. 10, 14, 37 and 39 was 425 or higher while that of glasses ofNos. 6B and 34 was 405 and 422, which were lower than 425. Thus, themicro Vickers hardness of the sealing glass to be used is preferably 425or higher.

The ferrite head was small in output and had problems in headperformance, but was 94% in the yield, 400 gf in the chip strength andmore than 500 hours in head breaking time and was high in reliability.In this way, according to the present invention, the same glass can beused between different kind of magnetic heads such as FTC head andferrite head. Accordingly, productivity can be markedly improved.

From the above, magnetic heads of high reliability can be obtained byusing the sealing glass of the present invention shown in Examples 1-4.Moreover, in order to obtain magnetic heads of high performance, themagnetic cores preferably comprise a support on which a magnetic film isformed, and more preferably the magnetic film is Fe-based magnetic film.Further, by making magnetic heads using the sealing glass of the presentinvention, the mass-production efficiency and the production yield canbe improved.

In this Example, the magnetic heads were maintained at a temperaturelower about 70° C. than the glass sealing temperature in the process ofmaking them. These magnetic heads were compared on the head chipstrength with those made without the above maintenance in cooling. Theglass of No.14 was used as the sealing glass. As a result, the head chipstrength of the magnetic heads maintained in cooling was higher about10% than that of the magnetic heads which were not maintained incooling. It is considered that this is because production of the fineparticles in the glass is accelerated by the maintenance in cooling andthe mechanical strength of the glass per se is improved.

Thus, in making magnetic heads using a glass containing rare earthelements as sealing glass, those of higher reliability can be obtainedby producing fine particles in the sealing glass, for example, by themethod of carrying out the heat treatment at a temperature lower thanthe glass filling temperature.

EXAMPLE 9

Three kinds of head chips of 100 μm, 65 μm and 55 μm in sliding widthwere prepared using Nos.10, 14, 6B and 79 as sealing glass. The chipstrength, head performance and head breaking time were evaluated in thesame manner as in Example 8. The results are shown in Table 14.

                                      TABLE 14                                    __________________________________________________________________________                  Head  Head breaking time (hr)                                                                      Apparatus performance                         Slinding                                                                             Chip                                                                              per-  Relative                                                                           Relative                                                                           Relative                                                                           Relative                                                                           Relative                                                                           Relative                            width Yield strength form- Tape speed speed speed speed speed speed                                                      No. (μm) (%) (gf) ance                                                    touch 11 (m/sec) 20 (m/sec)                                                   52 (m/sec) 11 (m/sec) 20                                                      (m/sec) 52 (m/sec)               __________________________________________________________________________    10 100 99 410 ◯                                                                    Δ                                                                          ⊚                                                                   ⊚                                                                   ⊚                                                                   Δ                                                                            Δ                                                                            Δ                             65 96 402 ◯ ◯ ⊚ ⊚                                                  ⊚ Δ                                                     ◯ ◯                                                     55 95 400 ◯                                                     ◯ .circleincircle                                                 . ⊚ .circleinc                                                 ircle. Δ ◯                                                  ◯                      14 100  98 388 ◯ Δ ⊚ ⊚                                                   ⊚ Δ                                                      Δ Δ                     65 94 386 ◯ ◯ ⊚ ⊚                                                  ⊚ Δ                                                     ◯ ◯                                                     55 94 387 ◯                                                     ◯ .circleincircle                                                 . ⊚ .circleinc                                                 ircle. Δ ◯                                                  ◯                      68 100  92 270 ◯ Δ ⊚ ⊚                                                   ⊚ Δ                                                      Δ Δ                     65 89 271 ◯ ◯ ⊚ 411 326 Δ                                                  X X                                 55 86 266 Δ ◯ 352 294 243 X X X                            79 100  76 216 ◯ Δ ⊚ ⊚                                                   450 Δ Δ X                                                           65 62 210 ◯                                                     ◯ 493 336 216                                                     Δ X X                         55 35 200 Δ ◯ 229 201 154 X X X                          __________________________________________________________________________

In view of the fact that magnetic recording and reproducingcharacteristics change depending on the state of contact between themagnetic head and the magnetic recording medium, the magnetic recordingand reproducing characteristics were evaluated in terms of tape touch.The mark "∘" means that the tape touch was good and "Δ" means that thetape touch was not good. The evaluation of apparatus was a syntheticevaluation of the characteristics obtained from the above parameters andoutput of the apparatus when the relative speed was changed to 11 m/sec,20 m/sec, and 52 m/sec. The mark "∘" shows that the results were good,"Δ" shows that problems remained in some of the parameters, and "x"shows that the samples could not be used as magnetic heads.

As for the magnetic heads made using the glasses Nos. 10 and 14, thesecould be made in high yields irrespective of the sliding width and had ahigh chip strength. Moreover, they are superior in head performance.Further, the head breaking time exceeded 500 hours even at a slidingwidth of 55 μm and a relative speed of 52 m/sec. In the case of thesliding width being 100 μm, the tape touch was inferior and the magneticrecording and reproducing characteristics were low, and the magneticheads had problems in this respect. Even when the sliding width was 65μm or more, there was a problem in the performance of apparatus at arelative speed of 11 m/sec.

On the other hand, as for the magnetic head made by bonding with No. 6B,occurrence of peeling at the glass bonding part or at the interface ofthe glass and the magnetic film increased with decrease in the slidingwidth at the time of making the head and the production yield decreased.The chip strength hardly changed since the core width was the same. Whenthe sliding width was 100 μm, the tape touch was inferior. When thesliding width was 65 μm, the head breaking time was less than 500 hoursat a relative speed of more than 20 m/sec. The magnetic head of 55 μm inthe sliding width was unstable in output and inferior in the headperformance. Moreover, the head breaking time was less than 500 hours.From the above, no good performances of apparatus were obtained whenthese magnetic heads were used. The magnetic head made by bonding withNo. 79 showed nearly the same characteristics as those of the magnetichead made using No. 6B and was not good.

As explained above, magnetic recording and reproducing apparatuses ofhigh performance can be obtained by mounting magnetic heads made usingthe sealing glass of the present invention shown in Examples 1-3. Morepreferably, the sliding width with the magnetic recording medium is 65μm or less. Furthermore, when the relative speed with the magneticrecording medium is 20 m/sec or more, magnetic recording and reproducingapparatuses of further higher performance can be obtained.

EXAMPLE 10

FIG. 21 shows such a type that a sealing glass was formed at a thicknessof about 0.3 mm by sputtering to perform bonding for a magnetic headcomprising magnetic cores 11, 11' of the single crystal ferritesubstrate of Example 8 and a magnetic film (Fe--Ta--C alloy) formedthereon by sputtering. This was somewhat lower than the type of Example8 in the bond strength, but had the similar sliding characteristics. Inthe figure, (332), (113) and (110) show the index of plane of eachsurface. It is preferred that at least 90% of each of the parts has suchindex of plane.

In this figure, the height H was 2.0 mm, the width C' was 2.0 mm, thethickness T was 140 μm, and the sliding width t of the tape sliding facewas 65 μm or 55 μm. The thickness T is preferably 0.05-0.1 time thewidth C'. The sliding width is further smaller for attaining furtherhigher recording density.

EXAMPLE 11

A magnetic head shown in FIG. 22 was made using the sealing glass of thepresent invention. In FIG. 22, 11, 11' indicate magnetic corescomprising an Mn--Zn ferrite substrate, 14, 14' indicate magnetic films,15 indicates a magnetic gap, and 16 indicates a sealing glass. In thisExample, the height H of head was 0.7 mm and the core thickness C' was1.5 mm. An Fe--Ta--C or Fe--Ta--N magnetic film having a saturatedmagnetic flux density of 1.0-1.5 T was used as the magnetic film. Themethod for making the magnetic head was the same as in Example 8, exceptthat the shape of the magnetic core was changed. The glass of No. 14 inTable 1 was used as the sealing glass and the bonding was carried out inthe same manner as in Example 9.

As shown in FIG. 22, in this magnetic head, the butting faces are onlyat the gap part and these butting faces were bonded with the sealingglass.

As shown in FIG. 23, this magnetic head was fitted to an exclusivefitting jig. The fitting jig was made of an Fe--C type soft magneticmaterial. In FIG. 23, 18 indicates a coil fitted to the magnetic head,19 indicates a fitting jig, and 20 indicates a terminal guiding hole forthe coil. The coil 18 previously wound several times was fitted to thelower end of the magnetic core 11. The magnetic head fitted with thecoil was fitted to the fitting jig and bonding was carried out. Theterminal of the coil was guided to outside through the terminal guidinghole 20.

Since the Fe--C type soft magnetic material used as the fitting jig waselectrically conductive, the static charge generated at the slidingcould be earthed. Further, deterioration of magnetic characteristics dueto the small head core could be prevented.

This magnetic head had such a structure that the part under the coilwinding window of the conventional magnetic head was omitted, and theheight H of the head was less than half that of the conventionalmagnetic head. Therefore, the weight of the magnetic head could bereduced to less than half. Thus, the power consumed by the motorrotating the cylinder could be reduced. Moreover, the sealing glass wasfilled in only the gap part and the two magnetic cores were bonded onlyby this sealing glass. Therefore, no sealing glass was filled in thepart under the coil winding window and it was difficult to make the headwithout using the high strength sealing glass of the present invention.

Since fitting of the coil is completed only by fitting the wound coil,the conventional coil winding step could be markedly simplified.Further, since the height of head was less than half that ofconventional ones, the time of cutting step could be reduced to abouthalf. When cutting was carried out more slowly than usual, working yieldof head chips could be improved and head chips of little chipping couldbe obtained.

EXAMPLE 12

FIG. 24 shows a schematic block diagram of a magnetic recording andreproducing apparatus mounted with the fitting jig fitted with themagnetic head obtained in Examples 8-10. Many video heads 21 which arethe magnetic heads used are fitted to cyclinder 22. The video head 21 isconnected with a control part comprising color signal processing part 23and luminance signal processing part 24 which process the informationcollected so that it can read the information from magnetic recordingtape 26 contained in cassette 25, and reproduce and record theinformation. Furthermore, the video head is connected to the drivingpart including motor 27 and motor driving part 28.

Recording and reproducing characteristics of this magnetic recording andreproducing apparatus were measured to find that it had goodcharacteristics. From the above, magnetic recording and reproducingapparatuses of high performance and high reliability could be producedin good mass-productivity and high yields.

As the tape 26, a metal vapor-deposited tape of more than 1000 Oe,preferably more than 1500 Oe in coercive force is used, and highreliability recording and erasion can be carried out by the magnetichead of this Example.

FIG. 25 is a partial sectional view of a revolving cylinder for tapeguide which constitutes the essential part of the present invention. Thereference numeral 101 indicates a revolving cylinder which guides themagnetic tape to contact with the outer peripheral face. The fixedcylinder has a guiding part to guide the magnetic tape in a helical formto the outer periphery and is fixed at a substrate which is not shown. Abearing means is provided at the fixed cylinder and is an axis which isfreely rotatably supported and a disk is bonded to the axis. Therevolving cylinder 101 is fixed at this disk. The numerals 110a, 110b(not shown, but provided at the position opposite to 110a at an angle of180°) indicate the heads for recording and reproducing the color signalsprovided for every field and comprise a magnetic thin plate such as offerrite forming a given head cap. These are respectively bonded andfixed to head bases 104a, 104b (not shown). The head bases 104a, 104bare fixed to the back side 102a of the head support 102 by screws 108aand 108b, respectively. 104a and 104b have the same shapes as 103a and103b, respectively. The numerals 111a, 111b similarly indicate the headsfor recording and reproducing the luminance signals provided for everyfield and are respectively bonded and fixed to head bases 103a, 103blike the head chips 110a, 110b for the color signals. The head base 103ais fixed to another face 102a of the head support 102 by screw 107a. Onthe other hand, the head base 104a is fixed by screw 108a to the face102b formed in the axial direction at a given space from the face 102aof the head support 102 in parallel to the face 102a. Since this headsupport 102 is formed so that there are no portions which project in theaxial direction from the faces 102a (front side) and 102b (back side),the size of thickness and parallelism of the faces 102a and 102b can behighly accurately and simply processed by lapping, etc.

FIG. 26 is a top view of a revolving cylinder mounted with a magnetichead of another example of the present invention. In the figure, (71A),(71B) show recording heads for sound signals, (72A), (72B) showreproducing heads for confirmation of recording of sound signals, (73A),(73B) show reproducing heads for sound signals, and (74A), (74B) showreproducing heads for sound signals at the time of variable speedreproduction of image signals. Further, (81) shows a recording andreproducing head for image signals, (82) shows a variable speedreproducing head for image signals, and (83) shows an erasing head forimage signals.

The number of the heads for recording and reproducing of sound signalsis eight in total and that of the heads for image signals is three, andit is impossible to provide the eleven heads in total in well-balancedstate especially in the arrangement of the recording and reproducingheads (81) for image signals and the variable speed reproducing heads(82). Therefore, as shown in this figure, a dummy head 90 for balancingis provided and the twelve heads in total are arranged at the sameintervals.

There are various combination in this arrangement. Furthermore, sixteenheads can be arranged with four in peripheral direction and four inlongitudinal direction.

This Example can be applied to the new development of high-vision. Table14 shows main specification of 32 inch direct vision type display andTable 15 shows main specification of extended definition projection typedisplay. The screen size of the latter is from 53 inch type to 250 inchtype and the scanning frequency is 35 kHz in horizontal direction ormulti-scanning of up to 70 kHz.

FIG. 27 is a standard system diagram of six screen high-visionmulti-system. The high vision signals are distributed to the respectivedisplays with extended definition (ED) signals by a high visionenlargement distributor and each display is of sequential scanning of525 scanning lines.

In a high vision for business use, the relative speed of a tape is 51.5m/sec or higher and a high head performance is required as mentionedabove. For public use, a relative speed of 20 m/sec or higher isrequired.

                  TABLE 15                                                        ______________________________________                                        Item              Specification                                               ______________________________________                                        Horizontal frequency                                                                            31.4 (ED)/33.75 (HD) kHz                                      Perpendicular frequency 60 Hz                                                 Horizontal resolution 800 TV (HD)                                             Perpendicular resolution 750 TV (HD)                                          Luminance (white peak) 720 cd/m                                               Size of screen 32 in.                                                         Aspect ratio 9:16                                                             Electric source AC 100 V, 50/60 Hz                                            Consumed power 300 W                                                        ______________________________________                                    

                                      TABLE 16                                    __________________________________________________________________________    Name of model                                                                        C53-3500R                                                                              C53-3510R                                                                              C85-4500R                                                                              C85-4510R                                   __________________________________________________________________________      Scanning                                                                      frequency                                                                     Hori- 24(15)˜35 kHz 24(15)˜70 kHz 24(15)˜35 kHz                                             24(15)˜70 kHz                           zontal (6 cycles) (15 cycles) (6 cycles) (15 cycles                           Perpen- 40˜120 Hz 40˜120 Hz 40˜120 Hz 40˜120 Hz       dicular (6 cycles) (15 cycles) (6 cycles) (15 cycles)                         Resolution                                                                    (100% display)                                                                Hori- 800 TV or more 800 TV or more 800 TV or more 800 TV or more                                              zontal                                       Perpen- 750 TV 750 TV 750 TV 750 TV                                           dicular                                                                       Luminance 410 cd/m.sup.2 540 cd/m.sup.2 240 cd/m.sup.2 340 cd/m.sup.2                                          (white peak)                                 Contrast ratio 140:1 or more 140:1 or more 140:1 or more 140:1 or more                                         Direct                                       vision range                                                                  Hori- 80° 90° 90° 90°                             zontal p-p p-p p-p p-p                                                        Perpen- 30° 30° 30° 30°                           dicular p-p p-p p-p p-p                                                       Screen size 53 in. 53 in. 65 in. 65 in.                                       (Aspect ratio) (9:16) (9:16) (9:16) (9:16)                                    Electric AC 100V, AC 100V, AC 100V, AC 100V,                                  source 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz                                    Consumed 420 W 550 W 420 W 550 W                                              power (800 VA) (800 VA) (600 VA) (800 VA)                                   __________________________________________________________________________    Name of model                                                                        C110-5000R                                                                            C110-5110R (HD)                                                                        C250-8510R                                                                            C250-8510 (with mirror)                       __________________________________________________________________________      Scanning                                                                      frequency                                                                     Hori- 24(15)˜35 kHz 15#75 kHz 24(15)˜7O kHz 24(15)˜7O                                     kHz                                             zontal (6 cycles) (10 cycles) (15 cycles) (15 cycles)                         Perpen- 40˜120 Hz 40˜120 Hz 40˜120 Hz 40˜120 Hz       dicular (6 cycles) (20 cycles) (15 cycles) (15 cycles)                        Resolution                                                                    (100% display)                                                                Hori- 800 TV or more 800 TV or more 800 TV or more 800 TV or more                                            zontal                                         Perpen- 750 TV 750 TV 750 TV 750 TV                                           dicular                                                                       Luminance 140 cd/m.sup.2 300 cd/m.sup.2 70 cd/m.sup.2 60 cd/m.sup.2                                          (white peak)                                   Contrast ratio 140:1 or more 80:1 140:1 or more 140:1                         Direct                                                                        vision range                                                                  Hori- 90° 90° 90° 90°                             zontal p-p p-p p-p p-p                                                        Perpen- 40° 40° 40° 40°                           dicular p-p p-p p-p p-p                                                       Screen size 110 in. 110 in. 250 in. 250 in.                                   (Aspect ratio) (9:16) (9:16) (9:16) (9:16)                                    Electric AC 100V, AC 100V, AC 100V, AC 100V,                                  source 50/60 Hz 50/60 Hz 50/60 Hz 50/60 Hz                                    Consumed 750 W 1,140 W 2,200 W 2,200 W                                        power (1,120 VA) (2,000 VA) (3,200 VA) (3,200 VA)                           __________________________________________________________________________

EXAMPLE 13

FIG. 28 shows one example of a schematic structural view of a 6 mmdigital VTR made in accordance with the present invention. Therespective signal processings and construction of the sliding systemaround the magnetic head were the same as those of FIG. 24. The imagesignals taken in through the optical system and the sound signals takenin through the microphone are transmitted to the writing head fitted tothe cylinder 22 and the audio head, respectively, thereby to-carry outwriting in the medium. The signal reproduction from the medium is sentto the reproducing terminal from the reading head.

EXAMPLE 14

FIG. 29 shows a schematic construction of one example of a 6 mm digitalvideocassette (6 mm-DVC) made in accordance with the present invention.In FIG. 29, 30 indicates a personal computer or a work station and 31indicates the 6 mm-DVC of the present invention. The image informationprepared in 30, such as computer graphics was recorded and stored in the6 mm-DVC. Furthermore, the information from the 6 mm-DVC was processedby the computer. By fitting to 31 a software having the informationobtained from FIG. 24, FIG. 27, etc. as a videocassette, the informationcould be processed by 30.

EXAMPLE 15

FIG. 30 shows a construction of a digital videocassette fitted to atransmission type electron microscope which was made in accordance withthe present invention. In this figure, 32 indicates a lens tube, 33indicates a specimen, 34 indicates a detector for electron rays, 35indicates a fiber cable, 36 indicates a digital videocassette, 37indicates a monitor, 38 indicates a digital printer, and 39 indicates anelectron ray. The intensity information of the electron ray which passedthrough the specimen is converted to photo-signals by the detector andis input in the digital videocassette 36. This information can be notonly microscopically examined with observing the screen of extendeddefinition by the monitor 37, but also printed to obtain an image ofextended definition over a photograph obtained by printing on aphotographic paper.

Simultaneously, analysis of the composition of the specimen could beconducted by collecting the information of characteristic X raysgenerated from the specimen and collecting in 36.

EXAMPLE 16

FIG. 31 shows a construction of a digital videocassette which was madein accordance with the present invention and fitted to a scanningelectron microscope. In this figure, 40 indicates a detector forsecondary ray, reflection electron, etc. In this case, too, images ofextended definition could be obtained as in the case of the transmissiontype electron microscope of FIG. 30.

According to the sealing glass of the present invention, mechanicalstrengths such as micro Vickers hardness and three-point bendingstrength can be greatly improved without increasing the characteristictemperature. Furthermore, when a structure is made using the sealingglass, glass bonding portions of high reliability equal to or higherthan those of the conventional glasses of high characteristictemperatures can be obtained even for the parts of low resistingtemperatures.

Furthermore, when magnetic heads are made by carrying out the bondingusing the sealing glass of the present invention at lower than theresisting temperature of magnetic films of high saturated magnetic fluxdensity such as those of Fe--C type, the resulting magnetic heads do notbreak even when the sliding width of the magnetic head and the magneticrecording medium is 65 μm and the relative speed with the magneticrecording medium is 20 m/sec or higher. Furthermore, by sliding themagnetic recording medium under the above conditions, magnetic heads andmagnetic recording and reproducing apparatuses having a high magneticrecording and reproducing characteristic and a high reliability can beprovided.

Moreover, the magnetic head having a novel construction according to thepresent invention can be reduced to less than half in its weight.Therefore, power consumed by the motor revolving the cylinder can bereduced. Besides, since fitting of coil is completed only by fitting awound coil into the magnetic head, the conventional coil winding stepcan be considerably simplified. Further, the height of head is less thanhalf that of the conventional heads and, hence, the time required forcutting can be shortened. Alternatively, by carrying out the cuttingmore slowly than usual, working yield of head chips can be improved andhead chips of less chipping can be obtained.

What is claimed is:
 1. A glass containing a matrix and particles,whereinsaid particles are dispersed in said matrix and said particlescontain a rare earth element, wherein the rare earth element is at leastone of Sc, Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, or Lu.
 2. A glassaccording to claim 1, wherein the glass is a borosilicate glasscomprising silicon oxide and containing boron, sodium and aluminum.
 3. Aglass according to claim 1, wherein the glass is a soda-lime glasscomprising silicon oxide and containing sodium and calcium.
 4. A glassaccording to claim 1, wherein the particles have a particle size of 1-50nm.
 5. A glass according to claim 1, wherein said matrix comprises aheavy metal oxide and one or more additional oxides selected from thegroup consisting of boron oxide and silicon oxide.
 6. A glass accordingto claim 1, said glass including, in terms of the following oxides, PbO,B₂ O₃, SiO₂, and Ln₂ O₃ (Ln being at least one of Sc, Y, Pr, Nd, Sm, Eu,Gd, Th, Dy, Ho, Er, Tm, Yb, or Lu).
 7. A glass according to claim 1,wherein the particles have a particle size of 3-10 nm.
 8. A glassaccording to claim 6, wherein said glass includes 30-93% by weight ofsaid PbO, 25% by weight or less of said B₂ O₃, 30% by weight or less ofsaid SiO₂, 6-50% by weight of said B₂ O₃ and said SiO₂ in total, and0.3-3.0% by weight of said Ln₂ O₃.
 9. A glass according to claim 1,wherein said particles are Ln₂ O₃.
 10. A glass according to claim 1,whereinsaid matrix includes filler material that reduces the thermalexpansion coefficient of the glass, and said filler material isdispersed in said matrix.
 11. A glass according to claim 10, whereinsaid filler material includes ZrSiO₄, PbTiO₃, β-eucryptite or quartzglass.
 12. A method of using a glass of claim 1 comprising the stepsof:heating the glass to melt; cooling the melted glass; and holdingtemperature of the glass lower than the melting temperature toaccelerate depositing of the particles.
 13. A method according to claim12, wherein the step of cooling has a 1-2° C./sec cooling speed.
 14. Amethod according to claim 13, wherein the step of holding temperatureincludes holding temperature at 70° C. lower than the meltingtemperature.
 15. The glass according to claim 1, wherein the rare earthelement is in the form of an element, an oxide, a compound, orcombinations thereof.
 16. A sealing glass containing a matrix andparticles, whereinsaid particles are dispersed in said matrix and saidparticles contain a rare earth element, wherein the rare earth elementis at least one of Sc, Y, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Tm, Yb, or Lu.17. A glass according to claim 5, wherein said heavy metal oxide is anoxide of lead.
 18. A sealing glass according to claim 16, wherein thesealing glass is stick shaped.
 19. A method of producing glasscomprising the steps of:mixing the ingredients of a glass; melting themixed ingredients; and depositing particles in the fusion; whereinsaidingredients include PbO, B₂ O₃, SiO₂, Ln₂ O₃ (Ln being at least one ofSc, Y, Pr, Nd, Sm, Eu, Gd, Th, Dy, Ho, Er, Tm, Yb or Lu); and saidparticles contain a rare earth element.
 20. A method according to claim19, whereinthe step of melting includes a step of stirring the fusion ofthe ingredients by ultrasonic waves.
 21. A method according to claim 19whereinthe step of depositing includes a step of cooling the fusion ofthe ingredients.
 22. A method according to claim 19, wherein saidingredients include, 30-93% by weight of said PbO, 25% by weight or lessof said B₂ O₃, 30% by weight or less of said SiO₂, 6-50% by weight ofsaid B₂ O₃ and said SiO₂ in total and 0.3-3.0% by weight of said Ln₂ O₃.23. A method of producing glass the steps of:providing the glass ofclaim 1 in broken form; mixing said broken glass with filler materialthat reduces the thermal expansion coefficient of said glass; sinteringsaid glass and said filler material.
 24. A method according to claim 23,wherein the step of sintering includes a step of heating the mixture ofsaid glass and said filler material.
 25. A structure comprising;asubstrate; and the sealing glass of claim 16, coated on the surface ofsaid substrate.
 26. A structure comprising;a pair of substrates; and thesealing glass of claim 16 which bonds said substrates.